Coffee is full of mythologies, pseudo-science, and half-baked hypotheses. Correlations are observed and are presumed to be causation. Quite a bit of food science follows this pattern (see the recent gluten reversal as an example). In the case of coffee storage, customers are told to put their seeds in the fridge or freezer to extend its shelf-life. Between a mixed truth and how popular this idea has become, we often have folks asking if these chilling appliances are appropriate for their storage needs. Let's put that answer aside for just a moment and explore what happens to coffee as it ages.
When sacks of green coffee arrive at the roastery, their life-clocks have already been ticking two to four months. It might be helpful to know that well-processed coffee isn't simply picked and sent post-haste to our roastery. There is a beneficial stage called processing that may involve depulping, enzymatic breakdown, and quite importantly - steady drying until the green seeds fall to roughly 11% moisture content. These unroasted seeds are constantly exchanging moisture with the air and whatever else surrounds it. For green coffee to be stable during its long journey to our roastery, it must be dried in an intentional, even, Goldilocks style way (not too hot & fast, not too cool & slow). Thoughtful, dedicated farmer-producers and their teams are crucial to these steps! That said, the aging of the green coffee might be seen as trivial compared to the staling spell roasting puts the beans under.
When a coffee order is placed, our roasting team gets to work, utilizing years of knowledge, skill, and experience to guide that coffee's journey from green to brown. As this happens though, they are setting into motion thousands of chemical and physical changes that propel the coffee down a path to its imminent stale demise. Now, this is absolutely a necessary evil! Without roasting, your cup of coffee wouldn't taste very good at all (it might even make you nauseated). That's because roasting involves taking many compounds through a conversion process, giving us great sweetness, liveliness, aroma, and body in our brews. Due to these conversions, many compounds prone to oxidation and other forms of breakdown are created. It calls to mind Tennyson's writing -
'Tis better to have loved and lost
Than never to have loved at all
We are definitely going to lose our coffee sooner once roasted, but oh is it worth it!
It is generally thought that a roasted coffee tastes good for two to four weeks. That's not a bad guideline to brew by, but as with most rules, it is a huge generality. So what are the factors that might skew this timeline? To find out, we dug deep into the internet and we put the same coffee (Kenya Gondo) through many different storage processes to see which preserved flavor and which ruined it.
Roast is a big factor in freshness. The more a green coffee is developed through roasting, either for a longer amount of time and/or through higher temperatures, the more prone it becomes to staling. This is due to both physical and chemical changes. One of the main physical changes is the increasing volume and porosity of the seed. Increasing roast development opens up the seed's pores to a greater degree. The result is that volatile aromatics, lipids, and carbon dioxide all diffuse at an accelerated rate. A more developed roast has also produced more free radicals within itself, meaning that it will naturally oxidize more quickly. The bottom line is that a lighter (read: denser) roast is going to stay fresh longer. That is not to say that lighter roasts are better, period. Utilizing this knowledge with an application towards different roast profiles is the key - understanding that darker roasts will taste better earlier off-roast (typically 1-2 weeks), while lighter roasts may stay tasting pretty good for several weeks (1-4 weeks). This same porosity difference is why more developed roasts often smell more pungent in their "wholeseed" form than do less developed roasts.
Brew method matters! We find that the espresso machine (with its high pressure brewing) allows us to get more out of our coffees later in their age (after three weeks) than handbrewed methods do. This principle affects the first week off-roast as well. Due the high amount of carbon dioxide being released from the grounds, which is created by Strecker degradation during roasting, espresso shots that are pulled earlier than a week off often taste sour and exhibit a boatload of crema. You might see all of this crema and think, "That looks great!" Unfortunately, this rampant crema creates that sour taste we mentioned through carbonic acid and misleading us visually into underextraction (which is why scales are the jam; they don't lie!). Handbrewed methods seem to get along better with super fresh roasts (1-4 days off), which probably has a lot to do with the carbon dioxide having somewhere to go (namely, the air).
Speaking of air, oxygen may be coffee's number one threat in terms of medium to long-term staling. From the moment the roaster catalyzes new compounds, oxygen gets busy breaking them down. Shortly after roasting, the seeds are putting off enough carbon dioxide to blunt the intake of the invading oxygen. As this carbon dioxide dissipation wanes, oxygen creeps in. As if staling weren't bad enough, oxygen also has the gall to turn coffee oil rancid. Remember that the more open a coffee's pores are, the faster the lipids will diffuse to the surface, becoming oxidized and turning rancid much more quickly. The bottom line is that keeping oxygen away from your coffee is an imperative to maintaining freshness. An airtight bag with a one-way air valve helps tremendously! Airtight canisters where the lid can be compressed do a great job too.
Moisture takes its own toll on a coffee's flavor. Coffee is hygroscopic, meaning it exchanges water freely with its environment. Put your coffee in the fridge or even leave the bag open for a while on a super humid day, and you'll notice a loss of volatile aromatics due to increased water exchange. In layman's terms, your coffee won't have as much of a distinctive aroma, which is the biggest contributor to flavor. For this reason, we do not recommend the refrigerator for storage. The pantry seems to do the trick. In our cupping, the fridge sample wasn't terrible, but wasn't good either.
Heat also breaks your coffee down by speeding up chemical processes. We do use high heat to roast the coffee, but just as too much roasting can ruin a batch, so can leaving your roasted seeds exposed to heat thereafter. The two biggest culprits here are direct sunlight and leaving a bag in the car on a hot day. We can tell you from experience that these issues cause more immediate harm to flavor than just about anything else, as the worst tasting sample in our experiment was the bag left in my car. The remedy is simple - don't leave your seeds exposed to sunlight or trapped in a hot car! Again, a cool, dry pantry is probably your best bet.
Now we come to freezing. The devil is in the details here. We cannot recommend that you put your bag into the freezer if you're going to take them out and put them back in several times. However, if you have a nice, airtight bag of coffee that you won't be able to drink for a while (maybe you're going on vacation or you just have too much coffee around), putting it into the freezer and thawing it once will preserve it quite well (although it does seem to fade rather quickly thereafter)! When we tasted these results, we were a little shocked, but the proof was in the cup! A clever trick for freezing might be to break a single bag down into ziplock baggies of individual portions. Freeze all of the little baggies, then remove only the baggie you need for that day. This will keep all the others nice and frozen until you are ready to use them. Even with this advantage, most of our guests in the cupping agreed that fresh, unfrozen was still the best.
The packaging also seems to have an effect. Our previously unopened and opened white Ceremony tie down bags showed quite well in the cupping. This is probably due to their well-sealed lining and its one-way air valve, which lets gas out, but not in. For occasional in-house use, we also have some thin metal composite bags. These do not have an air-valve, seemed to leak from various points, and did not show as well in the cupping. It's good to know that our elegant white retail bags are doing a good job! If you and we wanted to take our storage to the next level, we could do an inert gas flush (like nitrogen or argon) to the bag. We'll keep you all posted if this becomes a reality for us! I've heard that a gas flush into a freshly roasted coffee can easily extend shelf life of that unopened bag to five weeks. Here's to progress against staling!
In the end, the best storage practices are to look for a recent roast date, buy enough fresh coffee to get you through a week or two, place that coffee into a cool, dry pantry or cupboard, don't open the bag until the first day you're actually going to drink it, reseal it well/push the air out, and keep an eye on that roast date!
If you have any useful tips or tricks for storing your coffee, please let us know at firstname.lastname@example.org.
Until next time, happy brewing!